1. Field of the Invention
The present invention relates to a method for driving magnetic head that is used for modulating magnetic field in a magneto-optical disk drive and a driving circuit of the same.
2. Description of the Prior Art
A magneto-optical disk can have large capacity by magnetic field modulation record and have relatively high speed data transmission with high reliability (high retention), so it is considered to be one of major storage devices in the future. Along with the recent tendency to a large capacity, a surface recording type magneto-optical disk drive is under eager research and development, which has high speed data transmission performance supporting the large capacity.
The surface recording type magneto-optical disk drive utilizes a method of applying the magnetic field to a medium from the side to which the light is applied, so that a lens and a coil can be combined as a unit. Therefore, the coil can be compact and its inductance can be reduced. As a result, flux reversal speed of the magnetic head can be increased so that the data transmission speed can be faster.
However, the magnetic head of the surface recording type magneto-optical disk drive is made by a thin film technology such as plating into a size of a few hundreds of microns of diameter, so a dc resistance increases and heat is produced more. Though air flowing between the recording medium and the magnetic head can cool the magnetic head, the temperature of the magnetic head may rise over 100 degrees centigrade resulting in undesired heat damage to the recording medium or distortion in an optical system such as a lens. Accordingly, it is an important task to suppress the heat effectively.
In the conventional magneto-optical disk drive, a typical driving method utilizes a rectangular pulse voltage that is applied to the magnetic head so that current is forced to flow through the inductance element. In contrast, as disclosed in Japanese unexamined patent publication No. 54-25715 for example, magnetic recording for a magnetic disk or a magnetic tape adopts a driving method in which pulse current (intermittent current) is supplied to the magnetic head so that power consumption of the magnetic head is reduced.
Also concerning the recording method for a magneto-optical disk, there is a method utilizing pulsed magnetic field as disclosed in Japanese patent No. 2803841.
However, a magneto-optical disk is a removable recording medium. When magneto-optical disks are exposed to ambient air, dust can adhere to recording surfaces of them. In order to prevent the recording surface from being damaged by dust, it is preferable to rotate the magneto-optical disk in the state where the magnetic head (and an optical lens or others) is kept away from the recording surface of the magneto-optical disk by a few tens of microns. In this case, the light beam spot becomes larger than in the levitation method that utilizes a slider. Accordingly, the coil size of the magnetic head should be enlarged. As a result, inductance of the coil increases being proportional to entire flux generation, so the driving method in which pulse-like current is supplied to the magnetic head becomes difficult.